What is a radio altimeter?

• A. An electronic altimeter that determines the height of an aircraft above the terrain by measuring the time needed for a pulse of radio-frequency energy to travel from the aircraft to the ground and return.
• B. A device that measures airspeed using pitot pressure.
• C. A navigation instrument that shows magnetic heading.
• D. A weather instrument for upper atmosphere.

Answer: (A)

A radio altimeter is an electronic instrument that determines the aircraft’s height above the terrain by measuring the time it takes for a radio pulse to travel from the aircraft to the ground and back. By using the known speed of radio waves, the system converts this round‑trip time into a height above ground (radio altitude). This is different from a barometric altimeter, which uses air pressure to show altitude above mean sea level, and it’s especially useful during approach and low-altitude flight for obstacle clearance. The reading can be affected by ground reflections, terrain, water, or heavy precipitation, but it provides direct height above terrain rather than altitude above sea level. It does not measure airspeed, heading, or weather in the upper atmosphere.